Viv is a six-month-old female entire Italian Greyhound. She presented to the Animal Emergency Centre (AEC) with a non-weight-bearing lameness in her right forelimb after jumping off a couch.

Radiographs revealed a fracture of the distal radius and ulna. Analgesia was provided overnight, and fracture repair was performed the following day at the Veterinary Referral Hospital utilising external fixation.

One week after discharge, Viv presented again to the AEC in a collapsed state. Her owners reported lethargy and hyporexia since discharge. She had been confined at home and did not have any access to poisons. On physical examination, she had marked tachycardia, pale mucous membranes, absent capillary refill time, hypodynamic pulses, and was hypothermic. Mild dyspnea was present and thoracic auscultation was normal.

An intravenous catheter was placed, and blood was collected for a packed cell volume (PCV), total solids (TS), serum electrolytes, acid-base, venous blood gases, prothrombin time (PT), and activated partial thromboplastin time (APTT).

Her packed cell volume was 22% and total solids measured by refractometry were 34 g/L. Venous blood gases revealed a respiratory acidosis and a severe hyperlactatemia (lactate 11.7 mmol/L) metabolic acidosis. Electrolytes, PT, and APTT were normal.

Diagnosis

Acute hemorrhage was considered the most likely cause of moderate anaemia and hypoproteinaemia, with subsequent hypovolaemic shock. Treatment was commenced with lactated Ringer’s solution and hydroxyethyl starch (Voluven) boluses, to correct the hypovolaemia, followed by a whole blood transfusion.

Further diagnostics at the AEC included a complete blood count (CBC), serum biochemistry, thoracic radiographs, and limited abdominal and thoracic ultrasound using a focused assessment with sonography for trauma (FAST) technique. Mild regenerative anemia and mild thrombocytopenia were present on the CBC, and a mild increase in alkaline phosphatase and glucose, and a marked hypoproteinaemia were present on serum biochemistry. Moderate free fluid was identified in the pleural space and an increased mediastinal soft tissue density was seen on thoracic radiographs. A thoracocentesis was not performed.

Following stabilisation, Viv was transferred to the Veterinary Referral Hospital for further investigation. A full thoracic ultrasound revealed pleural fluid and mass lesions within the cranial mediastinum and right caudal, ventral thorax, with no evidence of vascular flow. The rest of the thorax was unremarkable. Thoracocentesis was performed and a serosanguinous fluid was recovered with a PCV and TS concentration consistent with blood. Thoracic computed tomography with contrast study demonstrated non-contrast enhancing soft tissue masses in the right caudal hemithorax and in the cranial mediastinum adjacent to the thymus. This was thought to be consistent with haematoma formation originating from the thymus. Based on the above findings, Viv was diagnosed with thymic hemorrhage.

Viv improved with supportive care and was discharged home after two days. She was treated the following day for haematuria and a delayed blood transfusion reaction was diagnosed. She was dressed for two days with lactated Ringer’s solution and she recovered uneventfully.

Discussion

The thymus is an organ of major immunological importance, being the site of maturation of T lymphocytes exported as precursors from the bone marrow. It is an organ that is present at birth and starts involuting after the onset of sexual maturity; usually between 6 – 12 months in dogs.

Thymic disease is an uncommon disease of dogs and cats. It occurs mostly in older animals and the most frequently seen conditions are thymic lymphoma and thymoma. Other conditions reported include thymic branchial cyst, thymic hyperplasia, thymic hemorrhage, and thymic amyloidosis.

While thymic hemorrhage is an uncommon condition, it occurs primarily in dogs and rarely in cats. It has been described in dogs younger than two years of age, most commonly between those of 3 and 9 months.

Presenting signs include a peracute to acute onset of lethargy, tachypnoea or dyspnoea, pallor, muffled heart sounds or decreased lung sounds, and sudden death. Anticoagulant rodenticide toxicosis is the most commonly reported cause of thymic hemorrhage, however, other reported aetiologies include trauma, dissecting aneurysm of the aorta, neoplasia, and idiopathic. The veterinary literature reporting thymic hemorrhage is limited to case reports where the prognosis for survival appears to be low; however, this may reflect a reporting bias.

It has been hypothesized that the involuting thymus in younger dogs is prone to hemorrhage. Two mechanisms have been proposed: 1) hemorrhage from acute hypertension since the thin-walled veins and arteries in an involuting thymus do not receive enough lateral supportive pressure from adjacent adipose and loose connective tissue; 2) mild trauma could cause overstretching of the neck leading to rupture of the vessels.

In the case reported here, disorders of secondary hemostasis (including anticoagulant rodenticide toxicosis) can be excluded as the PT and APTT were normal. The platelet count was normal eliminating thrombocytopenia as a cause of the hemorrhage; however, thrombocytopenia affecting primary hemostasis cannot be excluded. It is less likely that the traumatic episode a week prior would have directly caused the thymic hemorrhage since published case reports suggest that presentation tends to be peracute to acute and death is common within 24 hours. It is more plausible that a thymic cyst formed from the trauma and this cyst subsequently ruptured. Since, neither thoracic surgery nor histopathology was required as part of the case management an exact etiology was not determined.

References:

Coolman BR, Brewer WG, D’Andrea GH, Lenz SD. Severe idiopathic thymic haemorrhage in two littermate dogs. J Am Vet Med Assoc 1994;205:1152–1153.

Cronin KL, Williams J, Klose T. What is your diagnosis? Thymoma, thymic lymphoma, or possible hemorrhage in the cranial mediastinal reflection. J Am Vet Med Assoc 2011;238:1107-1108.

Day MJ. Review of thymic pathology in 30 cats and 36 dogs. J Small Anim Pract 1997;38:393–403.

Liggett AD, Thompson LJ, Frazier KS, et al. Thymic hematoma in juvenile dogs associated with anticoagulant rodenticide toxicoses. J Vet Diagn Invest 2002;14:416–419.

Rickman BH, Gurfield N. Thymic cystic degeneration, pseudoepitheliomatous hyperplasia and haemorrhage in a dog with brodifacoum toxicoses. Vet Pathol 2009;46:449–452.